Not even GNOME itself could ignore the GNOME 3 criticism for much longer. "As part of the planning for the DropOrFixFallbackMode feature, we've decided that we will compile a list of supported gnome-shell extensions. This will be a small list, focused on just bringing back some central 'classic' UX elements: classic alt tab, task bar, min/max buttons, main menu. To ensure that these extensions keep working, we will release them as a tarball, just like any other module."

You forgot one big chunk. Since the majority of Gnome 2 users also was Ubuntu users, they ended up with Unity.

And I guess you still have a large amount of user still on Gnome 2, using distributions with longer life cycle like RedHat, Debian and older LTS. So even more will move over time when support ends for those.